The present disclosure relates to waste treatment systems and to devices that can be used to accelerate the separation of solid particles or fluids. Also disclosed are methods of separation.
Wastewater from sewage or industrial wastes can include suspended particles and other fluids besides water. Waste treatment systems are designed to separate these undesirable wastes from the water. One form of treatment equipment is a large tank or vessel which is designed to provide a long residence time.
Sedimentation is the process by which suspended particles heavier than water are removed by gravitational settling to the bottom of such a tank. In addition, lighter-than-water fluids, such as fats or oils, will rise to the top of such a tank. A “settling tank” is the term generally used to describe a tank whose purpose is to remove the sediment that collects at the bottom of a tank. “Sludge” is the term generally used to describe the sedimented material itself. A “skim tank” is the term generally used to describe a tank that is used to capture such fluids that rise to the top of the tank.
FIG. 1 is a side cross-sectional view of one kind of conventional settling tank. The settling tank has an inlet in the center of the tank. Wastewater is distributed as uniformly as possible from the inlet. In the settling zone, water has a very low velocity, allowing suspended solids to sink due to gravity. This creates a sludge zone on the bottom of the tank. The resulting clarified water is captured in a decanting trough and exits the settling tank. A scraper arm on the bottom of the tank pushes the sludge into a sludge collecting trough, and the sludge is thus removed from the settling tank.
FIG. 2 is a side-cross-sectional view of one kind of conventional skim tank. Wastewater is distributed through an inlet in the center of the tank. Lighter-than-water fluid, such as oil will rise, while the water sinks. An oil outlet located at the top of the tank permits removal of the lighter-than-water fluids. A water outlet is located at the bottom of the tank. A skimming arm may be located at the top of the tank to push the lighter-than-water fluid into a collection area.
Stokes' law describes the settling velocity of a suspended particle. The settling velocity is affected by the mass density of the particle, the mass density of the fluid, the dynamic viscosity of the fluid, and the radius of the particle. Some types of particles are difficult to separate from water. This includes small particles, having a radius of less than 6 μm and particles whose density is very close to that of water.
It would be desirable to provide systems, devices, and methods that could accelerate the separation of undesirable waste products from water.